I looked to see if this was posted earlier and did not find it. My apologies if it was already posted.

After completing the game on Hard and unlocking the cheat codes, Start a new game on Easy. Go to any area with several enemies. Equip the Stone Prison armor ability and just keep spamming the left bumper. Turning the enemies to stone counts as hits but does NO DAMAGE. If it is a group of 5 or 6 enemies you get five of six combo hits each time. I ended up getting the achievement in no time at all.